CVE-2026-92811 in Browserless
Summary
by MITRE • 09/17/2026
browserless versions 1.44.0 through 2.56.7 fail to enforce file protocol restrictions in Playwright websocket endpoints, allowing authenticated token holders to read arbitrary files. Attackers can navigate Playwright-driven browsers to file scheme URLs and access files accessible to the container process despite the ALLOW_FILE_PROTOCOL setting defaulting to false.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in Browserless versions 1.44.0 through 2.56.7 represents a critical security flaw within the Playwright websocket endpoints, specifically concerning the enforcement of file protocol restrictions. This issue stems from an insufficient validation mechanism that fails to properly restrict access to local resources when navigating browsers driven by the service. Although the configuration setting ALLOW_FILE_PROTOCOL defaults to false, indicating an intent to block such accesses, the implementation contains a logical error that allows authenticated token holders to bypass this restriction. By manipulating websocket connections, attackers can instruct Playwright-driven browsers to navigate directly to file scheme URLs, effectively circumventing the intended security controls and gaining unauthorized access to local filesystem resources accessible by the container process.
From a technical perspective, the core of this vulnerability lies in how the browser automation engine handles navigation requests over the websocket interface. When an authenticated user provides a token that grants them control over a browser instance, they can send commands to navigate to URLs using the file:// scheme. The application fails to intercept or reject these specific protocol schemes before passing them to the underlying Chromium-based rendering engine. This lack of strict input validation allows the browser process to resolve local paths relative to its execution context. Since Browserless typically operates within a containerized environment, this means that any files readable by the user account running the container can be accessed and exfiltrated through the websocket channel. The flaw is particularly dangerous because it leverages legitimate authentication mechanisms; an attacker does not need to break encryption or bypass network firewalls but simply exploits the trust placed in authenticated sessions to perform unauthorized file reads.
The operational impact of this vulnerability is severe, primarily due to its potential for data exfiltration and lateral movement within containerized deployments. An attacker who obtains valid authentication tokens can read sensitive configuration files, environment variables stored on disk, source code repositories mounted into the container, or other private documents residing in accessible directories. This capability effectively neutralizes the isolation provided by the container runtime regarding local file access if those resources are not strictly permissioned at the operating system level. Furthermore, because Playwright is often used for automated testing and scraping, this vulnerability could be abused to steal session cookies stored on disk or extract credentials embedded in configuration files, leading to broader account compromise beyond just the Browserless service itself.
This flaw aligns with CWE-20 Improper Input Validation, as the application fails to verify that navigation requests adhere to a strict allowlist of permitted protocols. It also relates closely to CWE-434 Unrestricted Upload of File with Dangerous Type if one considers the broader context of file handling, but more accurately maps to CWE-78 OS Command Injection principles in terms of unintended execution contexts, though here it is specifically about unauthorized data access via CWE-284 Improper Access Control. In the MITRE ATT&CK framework, this behavior corresponds to T1083 File and Directory Discovery, where an adversary explores the local system for sensitive information. Additionally, since exploitation requires prior authentication, it falls under techniques associated with Initial Access or Credential Access depending on how the tokens were obtained, but primarily represents a privilege escalation from web application interaction to host-level file access via T1506 Post-Exploitation: File and Directory Discovery.
To mitigate this vulnerability, organizations running affected versions of Browserless must immediately upgrade to version 2.56.8 or later where the issue has been resolved. For environments that cannot be updated instantly, a temporary mitigation involves ensuring that the container process runs under a highly restricted user account with minimal file system permissions. This limits the scope of files an attacker can read even if they successfully exploit the websocket endpoint. Additionally, administrators should audit their deployment configurations to ensure that sensitive data is not stored in locations accessible by the application runtime and consider implementing network-level controls or reverse proxy rules that inspect websocket traffic for suspicious navigation patterns targeting file protocols. Regular security assessments focusing on input validation within automation tools are essential to prevent similar logic flaws from being exploited in production environments.